The natural history of swine influenza is being studied in Hawaii, where introduction of swine from other areas is limited and few herds are infected with lungworms. The objectives are to determine how swine influenza virus is maintained in nature between epidemics and to make observations on the interchange of influenza virus between swine and man. It now appears that epidemics of swine influenza occur on the island of Oahu at about 3-year intervals. In several herds not infected with lungworms, epidemics appeared to be autochthonous. These and other data support the hypothesis that swine influenza virus is maintained in certain herds through chronic or latent infections in breeding animals. Epidemics occur when herd immunity is low because of replacement of breeding stock. Some common factor, perhaps climate change, seems to trigger epidemics in infected herds. Serologic data suggest that swine influenza virus is rarely transmitted to humans. Antibodies to current human type A influenza viruses (H3N2) were prevalent in adult swine on Oahu and other Hawaiian islands, but absent in pigs under one year of age indicating that H3N viruses have not become established in swine in Hawaii. BIBLIOGRAPHIC REFERENCE: Wallace, G.: Swine Influenza and Lungworms. J. Infect. Dis. 135:490-492, 1977.